Medium temperature strength of alumina-based ceramic mold of hollow turbine blade manufactured by gelcasting

Using polyimide and aluminum phosphate as binders, the bending strength, thermal mass loss behavior, phase transformation after sintering and microstructure of the specimens were researched, by three point bending strength test, TG-DSC, XRD and SEM method. The results show that the polyimide produces binding effect by melting and crosslinking under 500℃, strength of specimens increases from 3 MPa to more than 5 MPa; while the strengthening effect vanishes, after polyimide is burned out at about 500℃ (heating rate: 30℃/h). The three aluminum phosphates (aluminum orthophosphate, aluminum metaphosphate and aluminum dihydrogen phosphate) increase the medium temperature bending strength (from almost zero to 0.2, 0.2 MPa and 0.8 MPa respectively) at 500℃. The strengthening effect of aluminum dihydrogen phosphate is the best, while aluminum orthophosphate and aluminum metaphosphate are equivalent. By infusing with dihydrogen phosphate solution, integral ceramic mold is fabricated successfully without shifting and fracture of cores.